WASHINGTON (Reuters) - Hundreds of government employees file in and out of the U.S. agency for auto safety in Washington every working day, investigating potentially dangerous vehicles and managing a $900 million annual budget.

But an administrator is not among them - nobody has been nominated to the top job since President Donald Trump took office.

Also missing from the roughly 550 people on the payroll of the National Highway Traffic Safety Administration, or NHTSA, are a permanent chief counsel, director for government affairs, chief financial officer and enforcement chief.

While a deputy administrator was appointed last week, slow progress in bringing in senior politically appointed officials has nearly frozen key decision-making at the agency, according to five former NHTSA officials, consumer groups, lawmakers and some business leaders.

They said that without leadership in place NHTSA has either pushed back or failed to act on rules setting new standards for improving how buses fare in rollover crashes, a system to remind passengers in rear seats to wear seat belts, and new tire standards.

Eight months into Trump’s presidency, senior positions in many government agencies across Washington remain vacant, including roles at the State Department, the Department of Energy, the Environmental Protection Agency and throughout the Transportation Department that oversees NHTSA.

Some of the vacancies are the result of Trump's efforts to slim down the federal bureaucracy. Others are simply waiting to be filled.

The White House blames Democrats for dragging out the confirmation process for its nominees, and says vetting picks has been more complicated than usual because many come from the business world rather than government.

While many companies applaud Trump's moves to roll back federal bureaucracy, some also complain that delays in bringing aboard political appointees is hindering government decisions that could impact business.

The frustration extends to some U.S. diplomats, private-sector lawyers and others who regularly deal with government agencies, according to interviews.

'IN A STALL'

In September, the U.S. Tire Manufacturers Association urged Trump in a letter to accelerate his efforts to nominate a NHTSA administrator so the agency can comply with a 2015 road safety law passed by Congress.

The law ordered NHTSA to write regulations setting minimum tire standards for fuel efficiency and traction in wet conditions and create an online database for consumers to check for tire recalls.

U.S. manufacturers and consumer groups support the regulations, drawn up in response to vehicle deaths linked to faulty tires, because they will raise standards and make the U.S. market less accessible to poorly made versions.

"We don’t want the U.S. to be kind of the dumping group for the really low technology because there isn’t a standard to meet," said Dan Zielinski, the association’s senior vice president.

Two former NHTSA leaders and consumer groups say the agency is also moving slowly on other regulatory issues, such as improving side impact standards.

"This agency is in a stall ... They are not going to do very much without political leadership," said Joan Claybrook, a former NHTSA administrator under President Jimmy Carter and a prominent consumer advocate.

NHTSA said in a statement Friday that safety is its top priority. The agency is "committed to meeting all obligations as required" by the 2015 law. NHTSA has an ongoing review of all regulatory actions as part of an administration-wide effort.

A White House spokeswoman declined to comment on NHTSA but said "capable and professional staff" are filling essential positions throughout the government on an acting basis until confirmations go through.

Leadership shortages extend beyond the NHTSA. The White House had by Oct. 4 nominated 387 political appointees for civilian positions in the executive branch and 160 have been confirmed by the U.S. Senate, according to the non-partisan Partnership for Public Service.

Both numbers were well below those in the first eight months under at least the last four presidents. In the same period of Barack Obama’s presidency, 497 candidates were nominated and 337 confirmed.

One senior administration official said it aims to have all top positions - those at the level of assistant secretary and above - nominated by year's end.

Still, some political appointee jobs are expected to stay empty, the White House spokeswoman said. "The federal government has grown unrestrained for decades because politicians have been too afraid to ‘drain the swamp'," she said.

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'BEHIND THE CURVE'

In many cases, dire warnings from opponents that Trump's delays in putting forward political nominations for approval would cause chaos have proven overblown.

But there are examples of government slowing down because mid-level employees do not have the authority or are unwilling to make decisions.

At the Committee on Foreign Investment in the United States (CFIUS), which analyzes proposed transactions to ensure they do not harm national security, private-sector lawyers complain of slow decisions on big deals.

"There is an unwillingness for the staff people to make a decision," said Michael Gershberg, a trade and investment attorney with Fried Frank.

A lobbyist who works on CFIUS deals said some companies have had to refile proposals because CFIUS failed to reach a decision within 75 days. That drives up legal and financing fees and creates uncertainty about the deal. Deals that have been refiled include a bid by Jack Ma's Ant Financial to buy MoneyGram <MGI.O> and Zhongwang USA's $2.33 billion bid for Aleris Corp <ALSD.PK>.

The Senate last week confirmed Heath Tarbert, who is expected to oversee CFIUS, as an assistant secretary of the Treasury.

At the State Department, only six of the top 40 jobs have been filled, and no confirmed officials are in place to run regional bureaus that handle foreign relations. Instead, they are in the hands of career diplomats with limited authority.

The United States does not have an ambassador in place in such key allied countries as South Korea, Jordan, Qatar and Saudi Arabia.

"We’re pretty much frozen in amber here,” one official said.

A congressional aide said it was hard to determine the precise impact of the vacancies.

But he added that U.S. policy in the North Korea missiles crisis would likely be helped by an ambassador in Seoul, a fully empowered assistant secretary of state for East Asia and an active special envoy for North Korea.

"That’s just one example in the region with the most prominent national security crisis, and really one of the most serious in a long time," he said.

Deputy Secretary of State John Sullivan, testifying in Congress on Sept. 26, addressed the slow pace of filling posts.

"We’re behind the curve. We should be ahead of the curve. And we’re doing all we can to catch up,” he said. “Our work is getting done. It would be better done if we had those positions filled.”